Engineering materials and their properties

Introduction

Material science and engineering plays a vital role in this modern age of science and technology. Various kinds of materials are used in industry, housing, agriculture, transportation, etc. to meet the plant and individual requirements.

The knowledge of materials and their properties is of great importance for a design engineer

A design engineer must be familiar with the effects which the manufacturing processes and heat treatment have on the properties of the materials

The engineering materials are mainly classified as

1. Metals and their alloys, such as iron, steel, copper, aluminium etc.

2. Non-metals such as glass, rubber, plastic etc.

Metals may further be classified as

Ferrous metals

The ferrous metals are those which have the iron as their main constituent, such as cast iron, wrought iron etc.

Non-ferrous metals

The non-ferrous metals are those which have metal other than iron as their main constituent, such as copper, aluminium, brass, tin, zinc etc.

Physical properties of metals

Physical properties are employed to describe the response of a material to imposed stimuli under conditions in which external forces are not concerned.

Physical properties include

a) Dimensions,

b) Appearance,

c) Colour,

d) Density,

e) Melting point,

f) Porosity,

g) structure, etc.

Dimensions

Dimensions of a material implies it’s size (length,breadth,width,diameter, etc.) and shape(square,circular,channel,anglesection, etc.)

Appearance

• Metals themselves have got different appearances e.g., aluminium is a silvery white metal where as copper appears brownish red.

• Appearance include lusture, colour and finish of a material.

• Lusture is the ability of a material to reflect light when finely polished. It is the brightness of a surface.

Colour

• The colour of the material is very helpful in identification of a metal. The colour of a metal depends upon the wavelength of the light that the material can absorb.

Density

• The density is the weight of unit volume of a material expressed in metric units.

• Density depends to some extent on the

a) Purity of material

b) Pour volume

c) Treatment, the material has received.

• Density helps differentiating between light and heavy metals even if they have same shape and any outer protective coating.

Melting point

• Melting point of a material is that temperature at which the solid metals change into molten state.

• One metal can be distinguished from the other on the basis of its melting point.

Porosity

• A metal is said to be porous if it has pores within it.

• Pores can absorb lubricant as in a sintered self-lubricating bearing.

• It is the ratio of total pore volume to bulk volume

Structure

• It means geometric relationships of material components.

• It also implies the arrangement of internal components of matter( electron structure, crystal structure, and micro structure )

Materials science

Chemical properties of metals

• A study of chemical properties of materials is necessary because most of engineering materials when they come in contact with other substances with which they can react, tend to suffer from chemical deterioration.

• The chemical properties describe the combining tendencies, corrosion characterstics, reactivity, solubilities, etc.of a substance.

• Some of the chemical properties of metals are

1. corrosion resistance

2. chemical composition

3. acidity or alkalinity

Corrosion

It is the deterioration of a material by chemical reaction with its environment.

Corrosion degrades material properties and reduces economic value of the material.

Corrosion attacks metals as well as non-metals. Corrosion of concrete by sulphates in soils is a common problem

Performance requirement

The material of which a part is composed must be capable of embodying or performing a part’s function without failure.

for example – a component part to be used in a furnace must be of that material which can withstand high temperatures.

While it is not always possible to assign quantitative values to these functional requirements, they must be related as precisely as possible to specified values of most closely applicable mechanical, physical, electrical or thermal properties.

Material’s reliability

Reliabiliy is the degree of probability that a product, and the material of which it is made, will remain stable enough to function in service for the intended life of the product without failure.

A material if it corrodes under certain conditions, then, it is neither stable nor reliable for those conditions.

Safety

A material must safely perform its function, otherwise, the failure of the product made out of it may be catastrophic in air-planes and high pressure systems. As another example, materials that gives off spark when struck are safety hazards in a coal mine.